The present invention relates to a severing arrangement in general, and more particularly to a severing arrangement for webs, particularly fabrics, of thermally severable materials.
It has already been recognized that some fabrics or other webs, particularly such containing a large proportion of thermoplastic material, if not made entirely from such thermoplastic material, can be severed by resorting to a heated severing tool which penetrates into the thermally severable material of the fabric or other web and thus subdivides the same into two or more pieces. Based on this recognition, it has already been proposed to mount the severing tool which is intended to sever the fabric or web for displacement between an extended and a retracted position, the severing tool being urged towards its extended position and being displaced towards its retracted position in dependence on the resistance which the material of the fabric or other web offers to the penetration of the heated severing portion of the severing tool into such material during the severing action of the severing portion.
An arrangement of the above-mentioned type has already been disclosed, for instance, in the German Patent DT-PS 2,315,333. As already mentioned before, the severing tool of this arrangement which has the heatable severing portion is urged towards its extended position in such a manner that, when the web is to be cut in the longitudinal direction thereof during the longitudinal advancement of the web, the plane along which the severing tool is displaced as it moves from the retracted position to the extended position thereof is parallel to the longitudinal axis of the web and the direction of such displacement is opposite to the direction of advancement of the web. In this arrangement, when the resistance of the web to the penetration of the severing portion of the severing tool exceeds a predetermined value, the severing tool is displaced in the advancing direction of the web towards its retracted position, which results in the energization of a heating circuit. As a result of such an energization, the heatable severing portion of the severing tool is raised in temperature, so that the severing action of the severing portion is improved and the tool element, which is urged towards its extended position will be displaced toward the latter contrary to the advancement direction of the web.
Experience with this arrangement has shown that it is possessed of certain disadvantages. So, for instance, it is a pronounced drawback of this arrangement that the heating circuit is constantly being switched on and off which, on the one hand, results in a considerable consumption of electric power. On the other hand, and even more importantly, the constant switching on and off results in a very irregular appearance of the edge of the web at which the severed regions of the web are separated from one another. Furthermore, should the severing action of the severing tool be insufficient despite the heating of the severing portion of the severing tool, then the advancing web would move past the severing tool without being severed thereby which would result either in incomplete or non-existent severance of the web or, worse still, in a damage to the severing arrangement.